1 files changed, 55 insertions, 0 deletions
diff --git a/src/day_6.rs b/src/day_6.rs
new file mode 100644
index 0000000..c9d7d86
--- /dev/null
+++ b/src/day_6.rs
@@ -0,0 +1,55 @@
+#[derive(Copy, Clone, Debug)]
+struct Fish(u8);
+
+fn simulate(swarm: &[Fish], days: usize) -> usize
+{
+    let mut new_count = [0; 2];
+    let mut count = [0; 7];
+    for fish in swarm {
+        count[fish.0 as usize] += 1;
+    }
+
+    let mut day = 0;
+    let mut birth = 0;
+    for i in 0..days {
+        let today = count[day] + new_count[birth];
+        new_count[birth] = count[day];
+        count[day] = today;
+        day = (day + 1) % 7;
+        birth = (birth + 1) % 2;
+    }
+
+    new_count.into_iter().sum::<usize>() + count.into_iter().sum::<usize>()
+}
+
+fn part1(swarm: &[Fish])
+{
+    println!("Solution to part 1: {}", simulate(swarm, 80));
+}
+
+fn part2(swarm: &[Fish])
+{
+    println!("Solution to part 2: {}", simulate(swarm, 256));
+}
+
+pub fn run(input: Vec<String>)
+{
+    let initial_swarm: Vec<Fish> = input
+        .iter()
+        .map(|s| s.split(',').map(|s| Fish::new(s.parse().unwrap())))
+        .flatten()
+        .collect();
+
+    part1(&initial_swarm);
+    part2(&initial_swarm);
+}
+
+impl Fish
+{
+    pub fn new(timer: u8) -> Self { Self(timer) }
+}
+
+impl Default for Fish
+{
+    fn default() -> Self { Self(8) }
+}